Rainbow Dam
Generating capacity: 36 megawatts
336 Rainbow Dam Road,
Great Falls, MT 59404
Rainbow Dam is an eight-unit hydroelectric plant on the Missouri River, about six miles northeast of Great Falls, Mont. The units have a total generating capacity of 36 megawatts. (One megawatt can satisfy the average energy needs of 750 households.)
Rainbow Dam, which began operation in 1910, is 1,055 feet long and 29 feet high. Its reservoir is 4 miles long and has a storage capacity of 1,050 acre-feet. The dam is classified as a “run-of-river” project because it can generate electricity using the water that flows down the river, without the need to store additional supplies. Immediately downstream from Rainbow Dam is Rainbow Falls, which has a drop of 47 feet. Further downstream is Horseshoe Falls, with a drop of 12 feet.
As part of its investment in the state, PPL Montana broke ground in October 2009 on a $230 million project that will increase by 70 percent the amount of clean, renewable power generated at the Rainbow.
The new turbine, big enough to power about 45,000 homes, will be housed in a new structure about 200 feet downstream of the old powerhouse. The water will flow through a new intake structure into a 2,300-foot power canal to a 25-foot diameter penstock that will deliver the water to the new hydro turbine-generator in the new powerhouse.
The new turbine will rotate slower and has wider flow passages and fewer rotating surfaces, making it easier for fish to pass through unharmed. The new intake structure will improve fish passage. The project is scheduled to be completed in 2012.
Rainbow Dam is one of eight hydroelectric plants and one reservoir along the Missouri and Madison Rivers covered under PPL Montana’s Project 2188 operating license. Through this license, PPL Montana works with state and federal agencies and private groups to implement a diverse array of environmental stewardship projects to protect habitats on or near the banks of the Missouri and Madison Rivers.
Rainbow Dam is part of the Great Falls Portage National Historic Landmark. It is located between PPL Montana’s Black Eagle and Cochrane Dams. The company also operates the Ryan and Morony Dams on the Missouri River near Great Falls.